An Alliance Resource Partners LP subsidiary is seeking to expand its underground coal mining operations in Pennsylvania, according to the state's Department of Environmental Protection.

Tunnel Ridge LLC wants to change 1,206.43 acres of its existing Tunnel Ridge mine underground permit area and subsidence control plan area in Washington County from development mining only to full extraction longwall mining.

Production at the mine fell to 1.5 million tons during the 2017 fourth quarter compared to 1.8 million tons in the year-ago period. The company said on its earnings call that Tunnel Ridge was affected by an equipment move in the quarter.

The Department of Environmental Protection will hold an informal public conference on the planned expansion April 10.